The dispensing (more particularly of an as precisely determined amount as possible), i.e. the dosing, of liquid or viscous dosing materials, for example, adhesives, paints, printing varnishes, conductive substances bound in a binder system such as soldering pastes, converter materials for LEDs etc. is intended for the targeted application of such dosing materials, for example on target surfaces. For instance, electronic circuit boards are specifically and precisely provided with conductive substances, replacing previously necessary time-consuming and costly processes, such as scraping processes, based on masking. A particular challenge consists in the high-precision delivery of the dosing materials to the target surface, i.e. at the right time, at the right place and in a precisely dosed quantity. This can be done, for example, in that drop-wise dispensing via the nozzle of a dosing system takes place, whereby the size and/or quantity of the drops is predetermined as precisely as possible through the effect of the nozzle. Alternatively the dosing material can be sprayed on in a jet or applied as a mist.
The challenge of high-precision dosing becomes even greater if the dosing material is not an easily flowing substance, with a similar consistency to that of water, but a relatively viscous medium. Examples of these are highly enriched adhesives, strongly pigment-enriched paints or varnishes with a high proportion of pigment etc. Particularly in the case of such material and/or in situations where dosing materials are to be applied, the dosing of which must be particularly finely adjusted, it is decisive that the nozzle closes at exactly the required moment. This results in a specific drop break-off of the drops ejected by the nozzle, thereby allowing as precise dosing as possible by way of as small drops as possible.
In DE 27 17 539 A1 devices for the dosing of liquid single component adhesives are described. In these devices needle valves actuated by compressed air are used.
An adhesive application device is also described in DE 31 08 793 C2 in which the adhesive drips downwards out of a nozzle opening, whereby to assist this via an annular gap outside the nozzle compressed air is emitted which carries along the adhesive. The nozzle opening can be closed by means of a nozzle needle that is attached to a piston and through this can be moved in position.
U.S. Pat. No. 7,694,855 B2 describes a dosing system with a pneumatic actuator system, which via a lever acts on a plunger that opens and closes an outlet opening of a nozzle.
In high-precision fine applications, especially in the field of micro-dosing and particularly in the field of the above dosing materials, such systems reach their technical limits, more particularly because of the too slow mechanics.